From 606c7193d5fbf8ea3dafc8a9468f719fbf1d7160 Mon Sep 17 00:00:00 2001 From: Dave Hansen Date: Fri, 6 Apr 2018 13:55:04 -0700 Subject: [PATCH] x86/mm: Undo double _PAGE_PSE clearing When clearing _PAGE_PRESENT on a huge page, we need to be careful to also clear _PAGE_PSE, otherwise it might still get confused for a valid large page table entry. We do that near the spot where we *set* _PAGE_PSE. That's fine, but it's unnecessary. pgprot_large_2_4k() already did it. BTW, I also noticed that pgprot_large_2_4k() and pgprot_4k_2_large() are not symmetric. pgprot_large_2_4k() clears _PAGE_PSE (because it is aliased to _PAGE_PAT) but pgprot_4k_2_large() does not put _PAGE_PSE back. Bummer. Also, add some comments and change "promote" to "move". "Promote" seems an odd word to move when we are logically moving a bit to a lower bit position. Also add an extra line return to make it clear to which line the comment applies. Signed-off-by: Dave Hansen Cc: Andrea Arcangeli Cc: Andy Lutomirski Cc: Arjan van de Ven Cc: Borislav Petkov Cc: Dan Williams Cc: David Woodhouse Cc: Greg Kroah-Hartman Cc: Hugh Dickins Cc: Josh Poimboeuf Cc: Juergen Gross Cc: Kees Cook Cc: Linus Torvalds Cc: Nadav Amit Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-mm@kvack.org Link: http://lkml.kernel.org/r/20180406205504.9B0F44A9@viggo.jf.intel.com Signed-off-by: Ingo Molnar --- arch/x86/mm/pageattr.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c index 4d369d5c04c5..d3442dfdfced 100644 --- a/arch/x86/mm/pageattr.c +++ b/arch/x86/mm/pageattr.c @@ -583,6 +583,7 @@ try_preserve_large_page(pte_t *kpte, unsigned long address, * up accordingly. */ old_pte = *kpte; + /* Clear PSE (aka _PAGE_PAT) and move PAT bit to correct position */ req_prot = pgprot_large_2_4k(old_prot); pgprot_val(req_prot) &= ~pgprot_val(cpa->mask_clr); @@ -597,8 +598,6 @@ try_preserve_large_page(pte_t *kpte, unsigned long address, req_prot = pgprot_clear_protnone_bits(req_prot); if (pgprot_val(req_prot) & _PAGE_PRESENT) pgprot_val(req_prot) |= _PAGE_PSE; - else - pgprot_val(req_prot) &= ~_PAGE_PSE; req_prot = canon_pgprot(req_prot); /* @@ -684,8 +683,12 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address, switch (level) { case PG_LEVEL_2M: ref_prot = pmd_pgprot(*(pmd_t *)kpte); - /* clear PSE and promote PAT bit to correct position */ + /* + * Clear PSE (aka _PAGE_PAT) and move + * PAT bit to correct position. + */ ref_prot = pgprot_large_2_4k(ref_prot); + ref_pfn = pmd_pfn(*(pmd_t *)kpte); break; -- 2.30.2